Establishing efficacy of a new experimental treatment in the 'gold standard' design

Provided that there are no ethical concerns, the comparison of an active drug with placebo in a randomized two-arm clinical trial provides the most convincing way to demonstrate the efficacy of a new experimental treatment. However, in a placebo-controlled clinical trial it is not sufficient to demonstrate merely a statistically significant treatment difference. Regulatory authorities strongly recommend to assess additionally whether the observed treatment difference is also of clinical relevance. The inherent issue is the necessity of the a priori definition of what constitutes a clinically relevant difference in efficacy. This problem can be solved in a three-arm study by including an active control group. We address the necessary conditions in the gold standard design which allow the claim of efficacy for the new treatment with particular focus on assay sensitivity.     

Sequential parallel comparison design for “gold standard” noninferiority trials with a prespecified margin

Three‐arm noninferiority trials (involving an experimental treatment, a reference treatment, and a placebo)—called the “gold standard” noninferiority trials—are conducted in patients with mental disorders whenever feasible, but often fail to show superiority of the experimental treatment and/or the reference treatment over the placebo. One possible reason is that some of the patients receiving the placebo show apparent improvement in the clinical condition. An approach to addressing this problem is the use of the sequential parallel comparison design (SPCD). Nonetheless, the SPCD has not yet been discussed in relation to gold standard noninferiority trials. In this article, our aim was to develop a hypothesis‐testing method and its corresponding sample size calculation method for gold standard noninferiority trials with the SPCD. In a simulation, we show that the proposed hypothesis‐testing method achieves the nominal type I error rate and power and that the proposed sample size calculation method has adequate power accuracy.     

The quality of clinical trials with Harpagophytum procumbens

OBJECTIVE: To examine systematically the quality of the clinical trials investigating the effectiveness of Harpagophytum products. METHODS: Literature searches and enquiries to experts identified 20 studies of treatment with various Harpagophytum products (powder, aqueous and ethanolic extracts) for exacerbations of chronic musculoskeletal pain. Eight were open uncontrolled observational studies, one comparing progress under treatment for pain in back, knee and hip pain. Two were open comparisons with conventional treatment, only one of which was randomised. Ten were double-blinded, randomised controlled comparisons, 8 with placebo and 2 with NSAID comparator treatments. Indices of the internal and external validities were examined by reference to a checklist to see how well the studies answered the questions: do Harpagophytum products work and do they work as well as more conventional comparator treatments? RESULTS: The uncontrolled trials, though providing useful preliminary estimates of the possible effect of treating various conditions, could not separate the effects of the Harpagophytum product from whatever placebo effect might have been exerted in the circumstances of the study. The 2 open comparisons were open to performance, detection and/or selection bias. Of the 8 randomised double blinded controlled comparisons with placebo, 6 were marred by lack of transparency, one could not provide definitive evidence from its pre-selected principal outcome measure, and one provided good quality evidence of a dose dependent superiority of effect over placebo, though this was with a product that is not generally available for clinical practice. One of the randomised controlled comparisons with comparator (Doloteffin versus rofecoxib) was intended only as a pilot and studied too few patients for definitive conclusions whereas the other did provide good evidence that the powder, Harpadol is not importantly less effective than the weak NSAID diacerhein. CONCLUSIONS: Evidence of effectiveness of Harpagophytum products is not transferrable from product to product. The results of some studies suggest some effectiveness for some products, but for none of the clinically available products is the quality of evidence totally satisfactory. It is better so far with products that contain at least 50 mg of harpagoside in the daily dosage than with products (which happen to be of ethanolic extraction) that contain less.     

Superior safety in noninferiority trials

Noninferiority of a new treatment to a reference treatment with respect to efficacy is usually associated with the superiority of the new treatment to the reference treatment with respect to other aspects not associated with efficacy. When the superiority of the new treatment to the reference treatment is with respect to a specified safety variable, it may be necessary to perform the between-treatment comparisons. The efficacy and safety comparisons may be considered separately or simultaneous comparisons may be performed. Here techniques are discussed for the simultaneous consideration of both aspects.     

Treatment effects of EGb 761 and cholinesterase inhibitors – why available studies do not demonstrate superiority of the latter

Based on simple comparisons of drug-placebo differences found in clinical trials, it has repeatedly been concluded that EGb 761 is less effective in the treatment of Alzheimer's disease than cholinesterase (ChE) inhibitors. However, the data of pivotal studies with both types of drugs show that drug-placebo differences in cognitive outcomes are more influenced by the degrees of deterioration of the placebo groups than by changes of the actively treated groups. Since the former are determined by characteristics of the patient samples and the therapeutic environment, but not by drug effects, it is concluded that direct comparisons of drug-placebo differences are inappropriate to assess the relative potencies of anti-dementia drugs. Comparisons have to take into account the different unspecific influences. The currently available data do not support the notion of superiority of ChE inhibitors over EGb 761.     

Efficacy of a comfrey root (Symphyti offic. radix) extract ointment in the treatment of patients with painful osteoarthritis of the knee: results of a double-blind, randomised, bicenter, placebo-controlled trial.

This randomised, double-blind, bicenter, placebo-controlled clinical trial investigated the effect of a daily application of 6g Kytta-Salbe f (3 x 2 g) over a 3 week period with patients suffering from painful osteoarthritis of the knee. The two hundred and twenty patients examined consisted of 153 women and 67 men of an average age of 57.9 years. On average, the complaints relating to osteoarthritis of the knee had persisted for 6.5 years. Two hundred and twenty patients were included in the Full Analysis Set (FAS) and safety collective, 186 (84.5%) in the Valid Case Analysis Set (VCAS) collective. In the course of the trial, the visual analog scale (VAS) total score (primary target value) in the verum group dropped by 51.6 mm (54.7%) and in the placebo group by 10.1 mm (10.7%). The average difference between the groups of 41.5 mm (95% confidence interval=34.8 to 48.2 mm) or 44.0% is significant (p<0.001). The significance is confirmed through the evaluation of the diary, the VCAS evaluation and the separate assessment of the two centres. This also applies to the separate assessment of the VAS total score following pain at rest and on movement. The WOMAC (Western Ontario and McMaster Universities) total score (secondary target value) also improved similar to the VAS total score. At the end of the trial, a reduction by 60.4 mm (58.0%) was recorded for the verum group and a reduction of 14.7 mm (14.1%) for the placebo group. The average group difference of 45.7 mm (95% confidence interval=37.1 to 54.3 mm) or 43.9% is significant (p<0.001). The difference between the treatment groups increased systematically and significantly, in parallel with the duration of the treatment. Thus, the superiority of the treatment with Kytta-Salbe f over that with the placebo is proven, even by means of the multi-factorial multivariate analysis for repetitive measurements. In respect of the explorative secondary target values SF-36 (quality of life), angle measurement (mobility of the knee), CGI (clinical global impression) and global assessment of efficacy by the physician and the patient, a significant superiority (p<0.001 each) of the verum group over the placebo group was also proven. The results suggest that the comfrey root extract ointment is well suited for the treatment of osteoarthritis of the knee. Pain is reduced, mobility of the knee improved and quality of life increased.     

Development and validation of the Vitiligo Extent Score for a Target Area (VESTA) to assess the treatment response of a target lesion

Since localized treatment for vitiligo is as essential as systemic treatment, a reliable instrument for target evaluation is needed besides those for whole body evaluation. We developed the Vitiligo Extent Score for a Target Area (VESTA) using reference images of both marginal and perifollicular repigmentation to measure the repigmentation rate (%) in a target lesion. In the validation study, a total of 65 dermatologists in 10 institutes evaluated 17 pairs of vitiligo images (pre‐ and post‐treatment) using both a rough estimate and the VESTA. The VESTA (concordance correlation coefficient: 0.949, 95% confidence interval [CI] 0.942–0.955) was significantly more accurate than the rough estimate (0.896, 95% CI: 0.883–0.908). It was also associated with better inter‐rater reliability over the rough estimate, albeit not significant. The VESTA can afford intuitive, convenient, and reliable assessment of the treatment response in a target area, and would be useful in clinical practice as well as retrospective studies.     

Noninferiority trials

Noninferiority trials are intended to show that the effect of a new treatment is not worse than that of an active control by more than a specified margin. These trials have a number of inherent weaknesses that superiority trials do not: no internal demonstration of assay sensitivity, no single conservative analysis approach, lack of protection from bias by blinding, and difficulty in specifying the noninferiority margin. Noninferiority trials may sometimes be necessary when a placebo group can not be ethically included, but it should be recognized that the results of such trials are not as credible as those from a superiority trial.     

A regulatory perspective on choice of margin and statistical inference issue in non-inferiority trials

Without a placebo arm, any non-inferiority inference involving assessment of the placebo effect under the active control trial setting is difficult. The statistical risk for falsely concluding non-inferiority cannot be evaluated unless the constancy assumption approximately holds that the effect of the active control under the historical trial setting where the control effect can be assessed carries to the noninferiority trial setting. The constancy assumption cannot be checked because of missing the placebo arm in the non-inferiority trial. Depending on how serious the violation of the assumption is thought to be, one may need to seek an alternative design strategy that includes a cushion for a very conservative non-inferiority analysis or shows superiority of the experimental treatment over the control. Determination of the non-inferiority margin depends on what objective the non-inferiority analysis is intended to achieve. The margin can be a fixed margin or a margin functionally defined. Between-trial differences always exist and need to be properly considered.     

Repeated confidence intervals in self-designing clinical trials and switching between noninferiority and superiority

In self-designing clinical trials, repeated confidence intervals are derived for the parameter of interest where the results of the independent study stages are combined using the generalized inverse chi-square-method. The confidence intervals can be calculated at each interim analysis and always hold the predefined overall nominal confidence level. Moreover, the confidence intervals calculated during the course of the trial are nested in the sense that a calculated interval is completely contained in all the previously calculated intervals. During the course of the self-designing trial the sample sizes as well as the number of study stages can be determined simultaneously in a completely adaptive way. The adaptive procedure allows an early stop for significance. The clinical trial may be originally designed either to show noninferiority or superiority. However, in each interim analysis, it is possible to change the planning from showing superiority to showing noninferiority or vice versa. Since the repeated confidence intervals are nested, there is no risk to loose the noninferiority once showed when, after an interim analysis, the trial is continued in an attempt to reach superiority. A simulation study investigates the behavior of the considered confidence intervals. The performance of the derived nested repeated confidence intervals is also demonstrated in examples showing both kinds of switching during an ongoing trial.     

Interval estimation of the mean difference in the analysis of over‐dispersed count data

This paper focuses on the development and study of the confidence interval procedures for mean difference between two treatments in the analysis of over‐dispersed count data in order to measure the efficacy of the experimental treatment over the standard treatment in clinical trials. In this study, two simple methods are proposed. One is based on a sandwich estimator of the variance of the regression estimator using the generalized estimating equations (GEEs) approach of Zeger and Liang (1986) and the other is based on an estimator of the variance of a ratio estimator (1977). We also develop three other procedures following the procedures studied by Newcombe (1998) and the procedure studied by Beal (1987). As assessed by Monte Carlo simulations, all the procedures have reasonably well coverage properties. Moreover, the interval procedure based on GEEs outperforms other interval procedures in the sense that it maintains the coverage very close to the nominal coverage level and that it has the shortest interval length, a satisfactory location property, and a very simple form, which can be easily implemented in the applied fields. Illustrative applications in the biological studies for these confidence interval procedures are also presented.     

Scheffy's Confidence Intervals in the Models of Analysis of Covariance

Scheffe's confidence intervals for linear functions of some subvectors of a vector of parameters are presented. The considered subvectors are such that covariance matrices of their estimators are known non-negative definite matrices multiplied by unknown positive constants. This property is characteristic of the least squares estimators of vectors of main and interaction effects in the analysis of covariance models of the following experimental designs: split-block, split-plot, completely randomized two-factor design and randomized complete block design. The formulas for confidence intervals for linear functions of vectors of main or interaction effects in the designs mentioned above are given in the paper. The practical example is given as an illustration.     

A remark on a paper by misra

MISRA (1978) sets confidence intervals for a double linear compound of multivariate normal regression coefficients by using ROY'S maximum root test criterion. The exact test statistic to be used is STUDENT'S t. The t statistic gives narrower confidence bounds than those given by ROY's maximum root statistic. A result given by MORRISON (1975, p. 18, equation 10) for profile analysis is also obtained by using the STUDENT'S t test.     

First-dose analgesic effect of the cyclo-oxygenase-2 selective inhibitor lumiracoxib in osteoarthritis of the knee: a randomized, double-blind, placebo-controlled comparison with celecoxib [NCT00267215]

Cyclo-oxygenase-2 selective inhibitors are frequently used to manage osteoarthritis. We compared the analgesic efficacy of the novel cyclo-oxygenase-2 selective inhibitor lumiracoxib (Prexige) versus placebo and celecoxib in patients with knee osteoarthritis. This seven day, double-blind, placebo and active comparator controlled, parallel group study included 364 patients aged > or = 50 years with moderate-to-severe symptomatic knee osteoarthritis. Patients received lumiracoxib 400 mg/day (four times the recommended chronic dose in osteoarthritis; n = 144), placebo (n = 75), or celecoxib 200 mg twice daily (n = 145). The primary variable was actual pain intensity difference (100 mm visual-analogue scale) between baseline and the mean of three hour and five hour assessments after the first dose. Actual pain intensity difference, average and worst pain, pain relief and functional status (Western Ontario and McMaster Universities Osteoarthritis Index [WOMAC]) were measured over seven days. Patients also completed a global evaluation of treatment effect at study end or premature discontinuation. For the primary variable, the superiority of lumiracoxib versus placebo, the noninferiority of lumiracoxib versus celecoxib, and the superiority of lumiracoxib versus celecoxib were assessed by closed test procedure adjusting for multiplicity, thereby maintaining the overall 5% significance level. In addition, celecoxib was assessed versus placebo in a predefined exploratory manner to assess trial sensitivity. Lumiracoxib provided better analgesia than placebo 3-5 hours after the first dose (P = 0.004) through to study end. The estimated difference between lumiracoxib and celecoxib 3-5 hours after the first dose was not significant (P = 0.185). Celecoxib was not significantly different from placebo in this analysis (P = 0.069). At study end 13.9% of lumiracoxib-treated patients reported complete pain relief versus 5.5% and 5.3% of celecoxib and placebo recipients, respectively. WOMAC total and subscales improved for both active treatments versus placebo except for difficulty in performing daily activities, for which celecoxib just failed to achieve significance (P = 0.056). In the patient's global evaluation of treatment effect, 58.1% of patients receiving lumiracoxib rated treatment as 'excellent' or 'good', versus 48.6% of celecoxib and 25.3% of placebo patients. Lumiracoxib was well tolerated. The overall incidence of adverse events was similar across treatment groups.     

Getting real with real-time qPCR: a case study of reference gene selection for morphological variation in <Emphasis Type="Italic">Drosophila melanogaster</Emphasis> wings

Accurate estimation of gene expression differences during development requires sensitive techniques combined with gold-standard normalization procedures. This is particularly true in the case of quantitative traits, where expression changes might be small. Nevertheless, systematic selection and validation of reference genes has been overlooked, even in Drosophila studies. Here, we tested the stability of six traditional reference genes across samples of imaginal wing disks from morphologically divergent strains of Drosophila melanogaster, in a two-class comparison: quantitative or qualitative variation in wing morphology. Overall, we identified and validated a pair of genes (RpL32 and Tbp) as being stably expressed in both experimental comparisons. These genes might be considered as a bona fide pair of reference genes for gene expression analyses of morphological divergence in D. melanogaster wings. They might also be taken as good candidates for experimental identification of stable reference genes in other morphological comparisons using Drosophila or other insect species. Besides, we found that some genes traditionally used as reference in qPCR experiments were not stably expressed in wing disks from the different fly strains. In fact, a significant bias was observed when the expression of three genes of interest, which are involved in the regulation of growth and patterning during imaginal wing development, was normalized with such putative reference genes. Our results demonstrate how inaccurate findings and opposite conclusions might be drawn if traditional reference genes are arbitrarily used for internal normalization without proper validation in the given experimental condition, a practice still common in qPCR experiments.     

A novel alternative to F-tests for ecological studies

Differences or similarities in the variance of fitness traits are crucial in several biological disciplines, e.g. ecological, toxicological, developmental and evolutionary studies. For example the variance of traits can be utilized as a biomarker of differences in environmental conditions. In the absence of environmental variability, the differences of the variance of a trait can be interpreted as differences of the genetic background. Several tests and transformations are utilized when testing differences between variances. There is, however, a biological tendency for the variance to scale proportionally to the square of the mean (scaling effect) which can considerably bias the results of the tests. We propose a novel method which allows for a more precise correction of the scaling effect and proper comparisons among treatment groups and between investigations. This is relevant for all data sets of distributions with different means and suggests the reanalysis of comparisons among treatment groups. This correction will provide a more reliable method when using bioindicators.     

A strategy for developing representative germplasm sets for systematic QTL validation,demonstrated for apple,peach, and sweet cherry

Horticultural crop improvement would benefit from a standardized, systematic, and statistically robust procedure for validating quantitative trait loci (QTLs) in germplasm relevant to breeding programs. Here, we describe and demonstrate a strategy for developing reference germplasm sets of perennial, clonally propagated crops, especially those with long juvenile periods. Germplasm is chosen to efficiently represent important members of larger pedigree-connected genepools. To facilitate validation of multiple QTLs, genome-wide representation of alleles is optimized for designated important breeding parents (IBPs) by estimating average allelic representation in relatives. The strategy and arising principles were demonstrated in a simulated germplasm set. Strong statistical power can be achieved with a carefully chosen germplasm set composed of IBPs, their numerous unselected progenies and close relatives, and all available founders and intermediate ancestors. Crop Reference Sets were developed in the marker-assisted breeding (MAB)-enabling “RosBREED” project as a base resource for QTL validation in US breeding germplasm of apple (Malus × domestica), peach (Prunus persica), and sweet cherry (Prunus avium) consisting of 467, 452, and 268 individuals, respectively. These sets adequately represent the most designated IBPs, have distinct advantages for QTL validation over other germplasm arrangements of equal size, and are recommended as a base resource for QTL validation by breeders of these US crops. The strategy described here can be used to develop efficient reference germplasm sets suiting other breeding genepools or to calculate the statistical power for QTL validation of germplasm sets already established.     

Phytotherapy for functional dyspepsia: A review of the clinical evidence for the herbal preparation STW 5

Functional gastrointestinal disorders such as functional (or non-ulcer) dyspepsia are characterized by a broad spectrum of symptoms referred to the upper abdomen without a detectable cause utilizing routine diagnostic measures. It is now believed that disordered gut function (including abnormalities like disturbances of motility such as postprandial fundic relaxation, gastric emptying and disturbed visceral sensory function) play a key role for the manifestation of these disorders. The underlying pathophysiology is not yet fully understood. However, the available data suggest that a number of factors may contribute to the manifestation of symptoms. These factors include environmental factors such as acute infections as trigger event, psychological stressors that may precede acute exacerbations and a genetic predisposition. Considering the large number of mechanisms, a treatment targeting a single mechanism is unlikely to be effective in all patients. Indeed, chemically defined treatments usually gain a 10–15% superiority over placebo. In recent years placebo-controlled studies have demonstrated superiority of a commercial multicomponent herbal preparation, STW 5, with the trade name Iberogast^® for the treatment of patients with functional dyspepsia and irritable bowel syndrome. This phytopharmacon is a combination of nine plant extracts each with a number of different active constituents. Pharmacological studies have shown different effects of the single plant extracts on the (molecular) mechanisms which are discussed as underlying the manifestation of symptoms. Various well-controlled clinical trials have independently confirmed clinical efficacy and safety.The clinically efficacy of this multicomponent herbal preparation questions the current trend of highly targeted drug molecules that usually target one single receptor population while it has not been shown that a single receptor group plays a pivotal role for the control of symptoms. Herbal medicines are obtained from various plants and contain complex extracts with a large number of different active substances. While there are only limited head-to-head comparisons with conventional chemically defined medications, the combination of extracts with various gastrointestinal active ingredients appears to be advantageous for a heterogenous condition such as functional dyspepsia.     

Stepwise Procedures under Unknown Variances for Toxicological Evaluation

Toxicological study is of practical importance in modern drug development. Proper statistical methodologies for toxicological evaluation of new developed drugs are undoubtedly necessary. In toxicological studies, it is practically desirable for a method to not declare the safety of a developed drug at a higher dosage prior to the declaration of the safety at lower dosages. Hsu and Berger 's stepwise confidence interval method was recently proposed for this purpose. Unfortunately, their procedure necessitates the homogeneity of variances among dosages, which is seldom satisfied in practice. In this article, via the application of the Stein 's two‐stage sampling method, we propose a stepwise confidence interval procedure for the same task without the homoscedasticity restriction. In addition, our procedure is shown to control its family‐wise type I error rate at the pre‐chosen nominal level. A simulation study will be conducted to compare our method, Hsu and Berger 's stepwise confidence interval method, and a single stage stepwise testing procedure based on Welch 's approximation. Our procedure is empirically shown to outperform Hsu and Berger 's procedure under heteroscedasticity and perform similarly with Welch 's procedure. An example will be used to illustrate our method.